In recent years, a thin film solar cell made from gas and formed with plasma CVD (Chemical Vapor Deposition) has been receiving attention. Examples of such thin film solar cell include a silicon-based thin film solar cell having a silicon-based thin film, a CIS compound thin film solar cell, and a CIGS compound thin film solar cell, which are being developed and expanded in production.
A thin film photoelectric conversion element forming such thin film solar cell is formed by stacking a semiconductor film and an electrode film on a substrate with plasma CVD, sputtering, vacuum vapor deposition or the like. In a thin film photoelectric conversion element, a semiconductor layer lying between two electrodes has a small thickness, so that a short-circuit is readily caused across the electrodes due to a pinhole in the semiconductor layer, resulting in lower power generation property.
In order to restore the property of such thin film solar cell, Japanese Patent Laying-Open No. 2000-323738 describes an invention of a reverse bias processing device for a solar cell module in which a reverse bias voltage is applied across electrodes of a solar battery cell to remove a short-circuit portion (pinhole).
The reverse bias processing device for a solar cell module described in Japanese Patent Laying-Open No. 2000-323738 characteristically includes probes of a plurality of stages which contact electrodes of solar battery cells of three or more stages adjacent to one another, raising and lowering means for raising and lowering the probes of the plurality of stages together, and a switch for selecting a pair of probes for applying a reverse bias voltage across electrodes of an arbitrary pair of the solar battery cells adjacent to each other from among the probes of the plurality of stages. After the probes are lowered to contact the electrodes of the solar battery cells, reverse bias processing on the solar battery cells of the plurality of stages can be carried out by switching the switch. As a result, the number of probe lowering operations that are the most time-consuming can be substantially reduced as compared to in the past, thereby improving overall efficiency of reverse bias processing.
FIGS. 7 and 8 are diagrams illustrating a conventional reverse bias processing device for photoelectric conversion elements. FIG. 7 is a schematic cross-sectional view of a conventional thin film photoelectric conversion module. FIG. 8 is an equivalent circuit diagram of the conventional thin film photoelectric conversion module.
As shown in FIG. 7, in a thin film photoelectric conversion module MD, photoelectric conversion elements D1 to D6 have a structure in which a surface electrode layer SL including a transparent conductive film made of SnO2 or the like, a semiconductor layer L including a photoelectric conversion layer, and a rear surface electrode layer RSL including metal and a transparent electrode are stacked on a transparent insulating substrate B made of glass or the like.
Surface electrode layer SL, semiconductor layer L, and rear surface electrode layer RSL are partially removed, to electrically connect surface electrodes S1, S2, S3, S4, S5, and S6 to rear surface electrodes RS2, RS3, RS4, RS5, RS6, and RS7, respectively. Photoelectric conversion elements D1 to D6 are thus connected in series.
The equivalent circuit in FIG. 8 shows photoelectric conversion elements D1 to D6, surface electrodes S1 to S6, and rear surface electrodes S1 to S7. In the device described in Japanese Patent Laying-Open No. 2000-323738, a reverse bias voltage is applied across rear surfaces electrode RS1 and rear surface electrode RS2, i.e., to photoelectric conversion element D1, to carry out reverse bias processing, then a reverse bias voltage is applied by the switch across rear surface electrode RS2 and rear surface electrode RS3, i.e., to photoelectric conversion element D2, to carry out reverse bias processing, and then reverse bias processing is successively carried out through photoelectric conversion element D6.
Japanese Patent Laying-Open No. 62-176173 discloses a configuration for carrying out reverse bias processing simultaneously on all of a plurality of photoelectric conversion elements connected in series    Patent Document 1: Japanese Patent Laying-Open No. 2000-323738    Patent Document 2: Japanese Patent Laying-Open No. 62-176173